Device and method for installing femoral prosthetic knee joint

ABSTRACT

Devices and method for performing replacement prosthetic knee surgery are disclosed in which a spacing means is introduced between the femur ( 1 ) and tibia ( 2 ) while the patella ( 9 ) is in place. The spacing means separates the femur ( 1 ) from the tibia ( 2 ) by an amount essentially equal to or greater than the required flexion gap ( 4 ). An alignment device ( 26 ) is used for performing femoral bone cuts, which device attaches temporarily to a fitted tibial plate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the U.S. National Phase under 35 U.S.C. §371 ofInternational Application PCT/EP2006/009811, filed Oct. 11, 2006.

During surgery for fitting a prosthetic knee joint, a number of bonecuts are made to allow placement and orientation of the femoralcomponent of the prosthesis, and to determine and form the joint gaps inextension and flexion 4 (see FIG. 1). The size and shape of these twogaps affect final orientation of the prosthesis, as well as jointtensioning and clearances.

Generally, the bone cuts are formed so that in extension the joint gapis perpendicular to the mechanical axis of the femur, while in flexionthe joint gap is such as to place the femoral component in eitherneutral or external rotation and assure proper patellar tracking withthe femoral component. To fit the femoral component the gaps created bythe bone resections in both flexion and extension should be ofdimensions to achieve the previous tension in between femur and tibia inflexion after the prosthesis is fitted. Therefore, the cuts must accountfor the thickness of the femoral and tibial prostheses, and so placed tomaintain tension in the joint, and so align properly the prosthesis.There is difficulty in the art with achieving the correct alignment offemoral cuts because cutting the bones requires effectively dismantlingthe joint so the knowledge of the previous tensions and orientation islost. When the cuts are incorrect, improper kinematics will arise as thejoint rotates in use, and accelerated wear patterns or possible jointdislocation may occur.

After the prosthesis has been fitted, it may be necessary to performsoft tissue balancing. After balancing the ligaments should have thesame tension in extension and flexion. The technique of soft tissuebalancing has to be mastered carefully. In balancing the soft tissue,the surgeon will make cuts to the ligaments and muscles. Inadequate softtissue balancing will lead to instability, pain and eventual failure.The soft tissue balancing has to be assessed several times so that theappropriate flexion and extension gap is achieved. Even when soft tissuebalancing has been optimised by the surgeon, the subject must stillundergo physiotherapy to regain a muscular tension corresponding to athe best possible joint movement.

There is a need in the art for a method and technique for fitting thefemoral component of a knee prosthesis which provides accurate bone cutsgiving a same height of the extension and flexion gap, and that reducesor avoids the need for soft tissue balancing.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a three dimensional view of the femur and tibia inextension, and the extension gap.

FIG. 2 depicts a three dimensional view of the femur and tibia inflexion, and the flexion gap.

FIG. 3 shows a three dimensional view of the femur and tibia in flexion,where the femur is disposed with transcondylal holes, and where thepatella is in place.

FIG. 4 shows a three dimensional view of the femur and tibia in flexion,spacing pins are placed in the transcondylal holes, and where thepatella is in place.

FIG. 5A shows a three dimensional view of a barbed pin.

FIG. 5B shows a profile view of the barbed pin of FIG. 5A.

FIG. 6A shows a three dimensional view of a spacer pin.

FIG. 6B shows a three dimensional view of a keeper.

FIG. 7 shows a three dimensional view of an alignment device of thepresent invention.

FIG. 8 shows a three dimensional view of the femur and tibia in flexion,where the femur is disposed with spacing means, and the tibial plate isfitted.

FIG. 9 shows a three dimensional view of a coupling means of analignment device disposed with a serrated cylindrical hole.

FIG. 10A shows a three dimensional view of a rack element of analignment device, provided with a serrated cylindrical protrusion.

FIG. 10B shows a detailed view of the serrated cylindrical protrusion ofFIG. 10A.

FIG. 11A shows a three dimensional view of a posterior femoral cuttingblock according to the invention.

FIG. 11B shows a front elevation view of the posterior femoral cuttingblock of FIG. 11A.

FIGS. 12A and B shows a three dimensional view of an alignment devicecoupled to a posterior femoral cutting block and secured to a tibialplate; 12A is a side view, 12B is a front view.

FIG. 13A shows a three dimensional view sliding bushing of the presentinvention.

FIGS. 13B to D show a front elevation of the bushing of FIG. 13A, eachview depicting a hole having a central axis at different angles.

FIG. 14A shows a three dimensional view of a posterior femoral cuttingblock attached to a coupled to an anterior femoral cutting block duringsurgery.

FIG. 14B shows the same device as FIG. 14A, including cutting theposterior end of the femur head.

FIG. 14C shows the same device as FIG. 14A, including cutting theanterior end of the femur head.

FIG. 14D shows a photograph of the device shown in FIG. 14A used duringsurgery, where the posterior end of the femur head is being cut.

FIG. 15 shows a three dimensional view of an anterior femoral cuttingblock.

FIG. 16A shows a three dimensional view of a distal femoral cuttingblock prior to mounting on a posterior femoral cutting block.

FIG. 16B shows a three dimensional view of a distal femoral cuttingblock attached to a posterior femoral cutting block.

FIG. 16C shows a three dimensional view of a distal femoral cuttingblock attached to the femur during cutting.

FIG. 17 shows a three dimensional view of a distal femoral cuttingblock.

FIG. 18 shows a photograph of the spacer pins and keeper, tibial plateduring surgery.

FIG. 19 shows a photograph of an alignment device coupled to a posteriorfemoral cutting block and secured to a tibial plate during surgery.

FIG. 20 shows a photograph of an alternative view from that shown inFIG. 19.

FIG. 21 shows a photograph of the surgeon inserting securing pins in tothe posterior femoral cutting block.

FIG. 22 shows a photograph of the surgeon aligning the anterior femoralcutting block.

FIG. 23 shows a three dimensional view of an alternative alignmentdevice attached to a posterior femoral cutting block.

SUMMARY OF THE INVENTION

One embodiment of the present invention is a device (spacing means) forassisting prosthetic knee surgery by maintaining a correct flexion gapbetween the femur and tibia while the knee is in flexion, said devicecomprising at least one elongate member (18) of dimensions forintroduction through a hole (10, 11) that passes from the anterior (14)end of a femoral condyle (5, 6) through to the posterior (15) end ofsaid condyle (5, 6), which member is provided with an adjustableprotrusion configured to protrude from the posterior (15) end of saidcondyle (5, 6) by an amount at least equal to the flexion gap (4).

Another embodiment of the present invention is a device as defined abovewherein:

-   -   said elongate member is a pin (18),    -   said adjustable protrusion is a threaded region (20) at least at        one end of said pin (18), and the device further comprises a        keeper (85) provided with a threaded hole (19) for engagement        with the thread (20) of said pin (18), said keeper configured to        abut with the posterior (15) end of said condyle (5, 6).

Another embodiment of the present invention is a device as defined abovewherein:

-   -   said elongate member is a pin (18),    -   said adjustable protrusion is region provided with a plurality        of inclined barbs (101), located at least at one end of the pin,        which barbs are configured to fold back upon on contact with an        entry side of the hole (10, 11), and open and abut against the        posterior (15) end of said condyle (5, 6) at an exit side of the        hole (10, 11).

Another embodiment of the present invention is a device as defined abovewherein the number of elongate members is two.

Another embodiment of the present invention is an alignment device (26)for aligning a block for cutting the posterior (15) femoral condyles (5,6) during prosthetic knee surgery, which device comprises:

(i) a securing means (23, 23′) for temporary attachment to a fittedtibial plate (7), which securing means fixes the position andorientation of the alignment device (26) relative to the tibial plate(7),

(ii) a coupling means (24) for temporary attachment to a posteriorfemoral cutting block (29), which coupling means prevents rotation ofthe posterior femoral cutting block (29), around a z-axis, where thez-axis is parallel to the intermedular femoral axis, and

(iii) an extending means (25) joining (i) and (ii), which extendingmeans is configured to adjust the distance between (i) and (ii) along ay-axis, where the y-axis is defined as being parallel to theintermedular tibial axis.

Another embodiment of the present invention is an alignment device (26)as defined above wherein the securing means comprises a pair of pins(23, 23′) configured for insertion into a corresponding pair of holes(22, 22′) present on the edge of the tibial plate (7).

Another embodiment of the present invention is an alignment device (26)as defined above wherein said coupling means permits displacement of theposterior femoral cutting block (29) parallel to the x-axis.

Another embodiment of the present invention is an alignment device (26)as defined above, wherein said coupling means is a finger-likeprotrusion having an upper surface disposed with a flat groove, whichgroove is configured to engage with a pointed ridge of a receivingelongate slot (30) present in said posterior femoral cutting block (29).

Another embodiment of the present invention is an alignment device (26)as defined above wherein said extending means (25) is connected to thecoupling means (24) by way of a cylindrical coupling that permitsrotation of the posterior femoral cutting block (29) around the y-axis.

Another embodiment of the present invention is an alignment device (26)as defined above wherein the extending means (25) comprises arack-and-pinion assembly where the rack element (27) carries thecoupling means (24), while the pinion (28) carries the securing means(23, 23′), or vice versa.

Another embodiment of the present invention is a posterior femoralcutting block (29) comprising one or more blade guides (31, 32), furthercomprising a receiving slot (30) configured to receive a coupling means(24) attached to an alignment device (26) as described above.

Another embodiment of the present invention is a posterior femoralcutting block (29) as defined above, wherein a plane of blade guide (31,32) is aligned with the x-z plane, and set at an angle of between −10and +10 deg around the x-axis.

Another embodiment of the present invention is a posterior femoralcutting block (29) as defined above, wherein the receiving slot (30)runs parallel to the blade guides (31, 32), and connects the front (33)of the block to the back (34).

Another embodiment of the present invention is a posterior femoralcutting block (29) as defined above, wherein said receiving slot (30) iswider than the coupling means (24), allowing the posterior femoralcutting block (29) to move parallel to the x-axis relative to thecoupling means (24) where the x-axis is perpendicular to the y-z plane.

Another embodiment of the present invention is a posterior femoralcutting block (29) as defined above, further comprising an intramedularfermoral rod guide (35), which rod guide comprises an elongate slot (44)oriented perpendicular to said receiving slot (30), and is configured toreceive an intramedular femoral rod, IM rod (38).

Another embodiment of the present invention is a posterior femoralcutting block (29) as defined above, wherein the rod guide (35) isconfigured to receive a sliding bushing (40), which bushing (40) isprovided with a hole (41) through which the IM rod (38) passes.

Another embodiment of the present invention is a posterior femoralcutting block (29) as defined above, further comprising the bushing asdefined above.

Another embodiment of the present invention is a posterior femoralcutting block (29) as defined above, wherein the central axis of saidhole (41) crosses a transverse axis (B-B′) of the bushing (40) by anglebetween −15 and 15 deg.

Another embodiment of the present invention is a posterior femoralcutting block (29) as defined above, comprising two or more holes (56,57), the central axis of which lie in an axis parallel to the y-axis,configured to receive two or more attachment means (48, 48″) of ananterior femoral cutting block (46) and distal femoral cutting block(50), such that a plane of the blade guide (47) of the anterior block(46) aligns with the x-z plane and a plane of the blade guide (51) ofthe distal block (50) aligns with the x-y plane.

Another embodiment of the present invention is a posterior femoralcutting block (29) as defined above, wherein said rod guide (35) is anelongate structure perpendicular to the width of the receiving slot (30)and disposed with one or more outer grooves (66) running in an axisparallel to the y-axis, said grooves configured to receive an attachmentmeans (94, 95) of a posterior femoral cutting block (29).

Another embodiment of the present invention is an anterior femoralcutting block (46) as defined above disposed with a blade guide (47),said block provided with an attachment means (48′, 48″, 94, 95) forattaching to the posterior femoral cutting block (29), which means (48′,48″, 94, 95) is configured to align a plane of the blade guide (47) withthe x-z plane.

Another embodiment of the present invention is an anterior femoralcutting block (46) as defined above wherein said plane is set at anangle between −10 and +10 deg around the x-axis.

Another embodiment of the present invention is a distal femoral cuttingblock (50) disposed with a blade guide (51), said block provided with anattachment means (52, 55) for joining the block to the posterior femoralcutting block (29), which means (52, 55) is configured to align a planeof the blade guide (51) with an x-y plane.

Another embodiment of the present invention is a kit comprising one ormore of the following:

-   -   at least one device (spacing means) as defined above,    -   an alignment device (26) as defined above,    -   a posterior femoral cutting block as defined above,    -   an anterior femoral cutting block (46) as defined above,    -   a distal femoral cutting block (50) as defined above.

Another embodiment of the present invention is a kit as defined above,further comprising a tibial plate (7) disposed with a receiving slot forreceiving the securing means (23, 23′) of the alignment device (26) asdefined above.

Another embodiment of the present invention is a kit as defined above,further comprising a knee prosthesis.

Another embodiment of the present invention is a method for performingreplacement prosthetic knee surgery, after fitting a tibial plate (7)comprising the steps:

-   -   tensioning the knee joint while in flexion, while the patella is        in place to obtain or reproduce the correct flexion gap,    -   maintaining the tension using an adjustable the spacing means        between the fitted tibial plate (7) and the femur, and    -   performing femoral bone cuts after the patella is moved to one        side.

Another embodiment of the present invention is a method as definedabove, further comprising the steps of:

-   -   making a hole (10, 11) in each femoral condyle, which hole        passes through the anterior region (14) of the femoral condyle        and exits though the posterior end (15),    -   inserting said spacing means through said holes (10, 11) so        introducing said spacing means into the flexion gap while the        patella is in place.

Another embodiment of the present invention is a method as definedabove, wherein said spacing means is as defined above.

Another embodiment of the present invention is a method as definedabove, further comprising the step of attaching a posterior femoralcutting block (29) to the tibial plate (7) using an alignment meanswhich permits movements by the posterior femoral cutting block (29)along a y-axis, along an x-axis, and permits rotation about x- andy-axes relative to a static tibial plate, where the y-axis is parallelto the intermedular tibial axis, and the x-axis is perpendicular to theplane of the y- and z-axes, where the z-axis is parallel to theintermedular femoral axis, which step is applied after the patella ismoved to one side.

Another embodiment of the present invention is a method as definedabove, wherein said alignment means is an alignment device as definedabove.

Another embodiment of the present invention is a method as definedabove, further comprising the step of securing the posterior femoralcutting block (29) to the femur in an aligned position using pins (65′,65″) inserted into the posterior femoral cutting block (29) and driveninto the femur.

Another embodiment of the present invention is a method as definedabove, wherein said posterior femoral cutting block is a device asdefined above.

Another embodiment of the present invention is a method as definedabove, further comprising the step of attaching an anterior femoralcutting block (46) disposed with a blade guide (47) to the posteriorfemoral cutting block (29), using a means which aligns the blade guide(47) with the x-y plane, and allows translational movement of theanterior femoral cutting block (46), along an axis parallel to they-axis.

Another embodiment of the present invention is a method as definedabove, wherein said anterior femoral cutting block is a device asdefined above.

DETAILED DESCRIPTION OF THE INVENTION

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as is commonly understood by one of skill in theart. All publications referenced herein are incorporated by referencethereto.

The articles “a” and “an” are used herein to refer to one or to morethan one, i.e. to at least one of the grammatical object of the article.By way of example, “a pin” means one pin or more than one pin.

Throughout this application, the term “about” is used to indicate that avalue includes the standard deviation of error for the device or methodbeing employed to determine the value.

The recitation of numerical ranges by endpoints includes all integernumbers and, where appropriate, fractions subsumed within that range(e.g. 1 to 5 can include 1, 2, 3, 4 when referring to, for example, anumber of pins, and can also include 1.5, 2, 2.75 and 3.80, whenreferring to, for example, an angle in degrees).

Reference is made in the description below to the drawings whichexemplify particular embodiments of the invention; they are not at allintended to be limiting. The skilled person may adapt the device andsubstituent components and features according to the common practices ofthe person skilled in the art.

The present invention relates to a method and device for providingaccurate bone cuts during fitting of the femoral component of a kneeprosthesis. With reference to FIGS. 1 and 2, the invention is based onavoiding the changes to the flexion gap 4 that arises when the patella 9(knee cap) is moved to one side during femoral cutting, when the knee isin flexion. The inventors have found that if a spacing means isintroduced between the femur 1 and tibia 2 while the patella 9 (FIG. 3)is in place, which spacing means maintains the distance between thefemur 1 from the tibia 2 by an amount essentially equal to or greaterthan the required flexion gap 4, the femoral bone cuts made after thepatella is moved to one side are so accurate that the soft tissuebalancing is avoided altogether or reduced.

The present invention also relates to an alignment device for performingfemoral bone cuts, which device attaches temporarily to a fitted tibialplate. The alignment device allows the surgeon accurately to cut theposterior femoral condyle to create the correct flexion gap 4 afterfitting, to make a distal resection that maintains the correct extensiongap 3 after fitting, and to make the required cut the anterior femoralcondyle. By referencing the cuts to the tibial plate, the cuts are madewith consideration to the femoral/tibial gaps.

Furthermore, the solid attachment by the present device to the tibialplate provides stable alignment of the cutting blocks. This is differentfrom devices of the art which do not use the tibial plate as a referenceor attach thereto, and thus rely more on the skill of the surgeon, onsoft tissue balancing and post operative physiotherapy.

When the spacing means is combined with the alignment device, theinventors have found that subjects do not require such extensivepost-operative physiotherapy as compared with prior art methods, and canbe discharged from hospital within a few days. This contrasts withexisting techniques and devices which normally require a long hospitalstay, and several weeks of post-operative treatment for the subject toreach the same state. The faster recovery time reduces the cost offitting a knee prosthesis due to less hospital overnight time; the riskof infection during hospitalisation is concomitantly reduced.

Spacing Means

Reference is made to FIGS. 3 and 4 in the foregoing description. Oneembodiment of the invention is a spacing means, configured forintroduction through the anterior 14 region of a femoral condyle 5, 6,which spacing means maintains and/or adjusts the tension between theposterior femoral condyles 5, 6 and a fitted tibial plate 7 while theknee is in flexion. The spacing means is generally adjusted to maintainthe flexion gap 4. The spacing means preferably comprises at least oneelongate member 18 of dimensions for introduction through a hole 10, 11that passes from the anterior 14 end of a femoral condyle 5, 6 throughto the posterior 15 end of said condyle 5, 6. The means furthercomprises an adjustable protrusion that is configured to protrude fromthe posterior 15 end of said condyle 5, 6 by an amount at least equal tothe flexion gap 4. Thus, when placed in the hole 10, 11, each adjustableprotrusion can contact the tibial plate 7. By adjusting the distance bywhich the protruding part extends from the posterior 15 end of saidcondyle 5, 6, the required gap between the femoral condyles 5, 6 andtibial plate 7 can be obtained and/or maintained. Preferably, the numberof spacing means is two, one for a hole in each of the condyles.Preferably two holes are made such that an imaginary line drawn betweenthe two holes is essentially at right angles to the intramedular femoralaxis. Preferably the passage of each hole is essentially perpendicularto the intramedular femoral axis. Preferably each hole is placed in themiddle of each femoral condyle.

According to one aspect of the invention, the above mentioned spacingmeans comprises:

-   -   an elongate member that is a cylindrical pin configured for        introduction through a hole 10, 11 that passes between the        anterior 14 region of a femoral condyle 5, 6 and the posterior        15 end of said condyle 5, 6,    -   an adjustable protrusion which is a serrated region, located at        least at one end of the pin, and    -   a keeper provided with a hole and ratchet mechanism for        engagement with the thread of said pin, said keeper configured        to attach and abut with the posterior 15 end of said condyle 5,        6. The body of the keeper is sufficiently thin so as not to        occupy the entire flexion gap.

In this configuration, the spacing means operates in a similar manner toa cable tie in that the movement of the serrated region is locked in onedirection by the rachet.

According to one aspect of the invention, the above mentioned spacingmeans comprises:

-   -   an elongate member that is a cylindrical pin 18 (FIGS. 5A and        5B) configured for introduction through a hole 10, 11 that        passes between the anterior 14 region of a femoral condyle 5, 6        and the posterior 15 end of said condyle 5, 6,    -   an adjustable protrusion which is region provided with a        plurality of inclined barbs 101, located at least at one end of        the pin, which barbs are configured to fold back upon on contact        with the entry side of the hole 10, 11, and open and abut        against the posterior 15 end of said condyle 5, 6 at the exit        side of the hole 10, 11. The barbed region allows the surgeon to        obtain and maintain the correct flexion gap, simply by applying        pressure on the elongate member in the direction required. As        the spacing means may not be withdrawn, it may be made from a        biodegradable material such as a described below. The adjustable        protrusion part may be removed by cutting or snapping off. The        barbs 101 are preferably an array of inclined fins. Barbs 101        which restrict a movement of an object in a cavity in one        direction are well known in the art e.g. from rawlplugs, from        nature; the skilled person may readily provide a spacing means        described herein with suitable barbs.

According to a preferred aspect of the invention, the spacing meanscomprises:

-   -   an elongate member that is a cylindrical pin 18 (FIG. 6A)        configured for introduction through a hole 10, 11 that passes        between the anterior 14 region of a femoral condyle 5, 6 and the        posterior 15 end of said condyle 5, 6,    -   an adjustable protrusion which is a threaded region 20, located        at least at one end of the pin 18, and    -   a keeper 85 (FIG. 6B) provided with a threaded hole 19 for        engagement with the thread of said pin, said keeper configured        to abut with the posterior 15 end of said condyle 5, 6. The body        of the keeper is sufficiently thin so as not to occupy the        entire flexion gap.

The pin 18 may apply the necessary tension between the femoral condyles5, 6 and tibial plate 7 when the pin is rotated; the distance betweenthe end of the pin and the engaged keeper extends or reduces during pinrotation. The necessary tension is generally that require to maintainthe flexion gap 3 or enlarge it. Once the required flexion gap ismaintained, the patella 9 can be moved aside, and the cuts made to thefemoral condyles 5, 6 in the knowledge that the flexion gap 3 will bemaintained while the surgeon measures the joint for making the necessarycuts. Optionally, the pin 18 can be provided with a coupling 21 for atool that facilitates rotation, such as an hexagonal end (shown in FIG.6A), or a hole.

By configuring the spacing means to enter the anterior 14 region of afemoral condyle, the patella 9 can remain fully in place duringtensioning. This overcomes the problems of the prior art, wheretensioning takes place through attachment of a device to the distal end17 of the femur 1. This necessitates removal of the patella 9 to gainaccess to an attachment point. However, once the patella 9 is removed,tensioning is made without the constraints of patella 9 ligaments 16,16′, and the skill and experience of the surgeon become crucial tocompensate for the loss of tension by said ligaments 16, 16′ and toachieve satisfactory results, unlike the present invention. With thisinvention the spacing means overcomes the balance problem by avoidingthe need to remove the patella 9.

The spacing means can be made from any material having suitablecompression strength, and meeting the requirements for surgicalinstrument biocompatibility. Such materials include, for example,stainless steel and titanium. According to one aspect of the invention,the pin and keeper arrangement is biodegradable, in which case, it ismay be made from biodegradable alloys (e.g. magnesium alloys) or polymer(e.g. polyglycolide (PGA), polylactide (PLA),poly(epsilon-caprolactone), poly(dioxanone),poly(lactide-co-glycolide)), or a combination of these.

Alignment Device

The following description are made with reference to FIGS. 7 and 8.Another embodiment of the present invention is an alignment device 26for cutting the posterior 15 femoral condyles 5, 6, which devicecomprises:

(i) a securing means 23, 23′ for temporary attachment to a fitted tibialplate 7,

(ii) a coupling means 24 for temporary attachment to posterior femoralcutting block 29,

(iii) an extending means 25 joining (i) and (ii), which extending meansis configured to adjust the distance along the y-axis between (i) and(ii), where the y-axis is defined as being parallel to the intermedulartibial axis.

Securing Means

The securing means 23, 23′ can be any which allows the alignment device26 to attach to the tibial plate 7, and which fixes the position andorientation of the alignment device 26 relative to the tibial plate 7.Thus, any movement by the tibial plate 7 or tibia 2 is transmitted tothe alignment device 26, and vice versa. The securing means can be aprotrusion shaped for insertion into a corresponding slot present on theedge of the tibial plate 7. Preferably the securing means comprises apair of pins 23, 23′ configured for insertion into a corresponding pairof holes 22, 22′ present on the edge of the tibial plate 7. Preferably,the securing means 23, 23′ orients the alignment device on the tibialplate 7 such that extending means 25 adjusts along the y-axis.Preferably the securing means 23, 23′ orients alignment device such thatthe longitudinal axis of the extending means is at 85, 86, 87, 88, 89,90, 91, 92, 93, 94 or 95 deg to the tibial plate, or at an angle betweenany two of the aforementioned angles. Preferably, it is at 90 deg.

Coupling Means

The coupling means 24 is any that allows the temporary attachment of aposterior femoral cutting block 29 so that said block is positioned atleast approximately to cut the posterior femoral condyles afterattachment. Generally the coupling means 24 is a finger like protrusionthat can couple with a receiving elongate slot on the posterior femoralcutting block 29. The coupling means brings the posterior femoralcutting block 29 in parallel alignment with the tibial plate (see alsoFIG. 10). It may prevent free rotation (i.e. prevent rolling) of theposterior femoral cutting block 29, around the z-axis, where the z-axisis parallel to the intermedular femoral axis. It may, however, permitlimited rotation of the cutting block 29 about the x-axis, i.e. it mayallow tilting (pitching) of the block 29 to provide angled cuts. It mayalso permit limited rotation of the posterior femoral cutting block 29around the y-axis, i.e. it may allow the cutting block to yaw. Thecoupling means may permit lateral (side-to-side) displacement of theposterior femoral cutting block 29 relative to the tibial plate i.e.movement parallel to the x-axis, where the x-axis is perpendicular tothe plane of the y and z-axis. In one embodiment, the coupling means 24is a finger-like protrusion with a flat surface which surface contacts areceiving elongate slot 30 in the posterior femoral cutting block 29. Ina preferred embodiment, the coupling means 24 is a finger-likeprotrusion having an upper surface disposed with a flat groove 45, whichgroove 45 engages a pointed ridge present in the receiving elongate slot30. The ridge and groove arrangement allows the cutting block 29 topivot around the x-axis relative to the alignment device 26. Theelongate slot 30 is preferably wider than the coupling means 24, so theposterior femoral cutting block 29 can move laterally (parallel to thex-axis) relative to the coupling means 24. A locking mechanism may bepresent in the posterior femoral cutting block 29 to secure thealignment device 26, which mechanism may lock a preferred lateralplacement.

Extending Means

The extending means 25 adjusts the distance between the coupling 23, 23′and securing means 24 along a linear axis. The linear axis of theadjustment is normally parallel to the y-axis. Preferably, the extendingmeans 25 prevents any other displacement or rotation movement betweenthe coupling 23, 23′ and securing means 24. However, it may permit astep-wise rotation of the coupling means 23, 23′ relative to thesecuring means 24 by way of serrated joints as explained further below.The extending means 25 positions the posterior femoral cutting block 29over the posterior femoral condyles. By extending or contracting themeans 25, the surgeon can precisely select the amount of bone to removefrom the posterior surface of the femoral condyles.

The extending mechanism of the extending means 25 can be any. It shouldenable a precise control of the distance between the tibial plate 7 andthe posterior femoral cutting block 29, which distance can be lockedduring cutting.

According to a preferred embodiment of the invention, the extendingmeans comprises a rack-and-pinion assembly as shown in FIG. 7. The rackelement 27 may carry the coupling means 24, while the pinion part(obscured in the FIG. 28 may carry the securing means 23, 23′, or viceversa. The rack element 27 is normally oriented parallel to the y-axis.The invention also includes variants where rack element is set at anangle to the y-axis. Rotation of the pinion 28, for example by theinsertion of a turning handle 39 brings about the required change indistance between the coupling means 24 and securing means 23, 23′. Otherelements can be present within the extending means, which allow finecontrol of pinion rotation e.g. a rachet system 77 as seen in FIGS. 12A,12B, and 19.

In another preferred embodiment, the extending means 25 is connected tothe coupling means 24 by way of a cylindrical coupling. The cylindricalcoupling comprises a cylindrical protrusion in either the extendingmeans 25 or coupling means 24 that can be received by a cylindrical holein the other component. This arrangement allows the coupling means 24 torotate (FIG. 19, 76) around the extending means. This will permit theposterior femoral cutting block 29 to yaw i.e. to rotate about they-axis. The cylindrical coupling may further be provided with a lockingmeans to hold securely the desired yaw position of the cutting block.

In another preferred embodiment of the invention, the cylindricalprotrusion 70 is present on the rack element 27 of the extending means24. Preferably, the cylindrical protrusion 70 is at least partlyserrated as shown in FIGS. 10A and 10B. It may be provided withregularly spaced grooves 72 and ridges 73 that run parallel to thelongitudinal axis 74 of the cylindrical protrusion 70. The cylindricalhole 71 is reciprocally serrated as shown in FIG. 9, such that therespective ridges 73, 73′ and grooves 72, 72′ interlock when thecoupling means 24 is connected to the extending means 25. Thearrangement prevents the posterior femoral cutting block 29 from freelyrotating about the y-axis owing to the interlocking grooves and ridges,but allows the desired orientation about the y-axis to be chosen byremoving and repositioning the coupling means 24.

In the embodiment shown in FIGS. 10A and 10B, the cylindrical protrusionis extended along its longitudinal axis by a serrated upper 75 element,having an incomplete cylindrical surface. In other words, the roundsurface of the cylinder is disposed less than 360 deg around its centralaxis 74. In FIG. 10B, the cylinder is disposed by angle alpha around thecentral axis 74. Angle alpha may be 100, 110, 120, 130, 140, 150, 160,170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, 300,310, 320, 330, 340 deg, or a value in the range between any two of theaforementioned values.

The grooves 72″ and ridges 73″ of the upper element 75 preferably alignwith the ridges and grooves of the cylindrical protrusion 70.

Because the cylinder is incomplete in the upper element 75, the couplingmeans 24 can be engaged with the serrations (i.e. grooves 72″ and ridges73″) of the upper element 75 by moving the coupling means 24 towards theserrated part of the upper element 75. The coupling means 24 can also byeasily released by moving coupling means 24 away from the serrated partof the upper element 75. The movement required temporarily to release orlock the coupling means 24 is a convenient translation movement withinthe x-z plane, as opposed to an up-down movement along the y-axis. Oncethe correct angle with respect to the y-axis has been obtained, thecoupling means 24 can be pushed down to engage with the full cylindricalprotrusion 70.

The alignment device 26 is temporarily attachable to both the tibialplate 7 and posterior femoral cutting block 29. Once the cutting blockis properly aligned, the alignment device 26 can be removed, leaving thecutting block in place, held, for example, by securing pins driven intothe femur. With the removal of the alignment device, the surgeon's viewand freedom of movement is unobstructed, so enabling efficientresectioning using the mounted posterior femoral cutting block 29.

Tibial Plate

The tibial plate has the elements of a conventional tibial plate, inaddition to a receiving slot on the perimeter edge. The receiving slotreceives the securing means 23, 23′ of the alignment device 26. Thisallows the alignment device 26 to attach to the tibial plate 7, and tofix the position and orientation of the alignment device 26 relative tothe tibial plate 7.

Thus, any movement by the tibial plate 7 or tibia 2 is transmitted tothe alignment device 26, and vice versa. The receiving slot can be anyslot for receiving a corresponding protrusion present on the alignmentdevice. Preferably the tibial plate comprises a pair of holes 22, 22′present on the edge of the tibial plate 7 configured to receive acorresponding pair of pins 23, 23′ present on the alignment device 26.

Posterior Femoral Cutting Block

Reference is made in the following description to FIGS. 11A, 11B, 12Aand 12B. The posterior femoral cutting block 29 is a typical surgicalfemoral cutting block comprising a plurality of blade guides 31, 32, forvisual alignment of the block against the condyles and to receive andguide a cutting blade. As already described above, the posterior femoralcutting block 29, also comprises a receiving slot 30 that receives thecoupling means 24 attached to the alignment device 26. The receivingslot 30 preferably runs parallel to the blade guides in the x-axisdirection, connecting the front 33 of the block to the back 34.

In additional to the receiving slot 30, the cutting block 29 maycomprise an intramedular fermoral rod guide 35. Said rod guide 35comprises an elongate slot 44 oriented perpendicular to theaforementioned receiving slot 30, configured to receive an intramedularfemoral rod (IM rod) 38. The IM rod 38 passes through said slot. The IMrod 38 and rod guide 35 provide additional stabilisation to the cuttingblock 29 during alignment. The rod guide 35 permits upward 36 ordownward 37 movement of the IM rod-mounted cutting block 29 duringalignment, in concert with the extension or contraction of the extendingmeans 25. An advantage of allowing the cutting block 29 to movelaterally (parallel to the x-axis) relative to the coupling means 24 isthe that the IM rod can be mounted by the cutting block 29 even when thecoupling means 24 does not align with the IM rod 38.

FIGS. 12A and 12B show the posterior femoral cutting block 29 attachedto the alignment device 26 which in turn is attached to the tibial plate7. The alignment device moves along the y-axis as indicated by referencesign 81 in FIGS. 12A and 12B, by turning rachet 77 using handle 39. Thisallows alignment of posterior femoral cutting block 29 on the femur 1,relative to the tibial plate 7 or tibia 2. The posterior femoral cuttingblock 29 may pitch i.e. pivot around the x-axis in a limited manner asindicated by reference sign 80. The posterior femoral cutting block 29may also be displaced along the x-axis relative to the tibial plate 7 ortibia 2, as indicated by reference sign 63. The posterior femoralcutting block 29 may also rotate around the y-axis relative to thetibial plate 7 or tibia 2 (see FIG. 19, reference sign 76). Thus thecombination of the posterior femoral cutting block 29 attached to thealignment device 26 in situ permits precise control and movement ofposterior femoral cutting block 29 along and around several axis,permitting the surgeon to find the precise alignment relative to thetibia. Once aligned, the posterior femoral cutting block 29 may besecured on the femur using one or more pins 65′.

A further embodiment of the present invention, depicted in FIG. 23, is aposterior femoral cutting block 29, wherein said rod guide 35 is anelongate structure perpendicular to the width of the receiving slot 30and disposed with one or more outer grooves 66 running in an axisparallel to the y-axis, said grooves configured to receive an attachmentmeans 94, 95 of a posterior femoral cutting block 29 (see below).

The grooves 66 allow the posterior femoral cutting block 29 to attachsecurely to the anterior femoral cutting block 46. When the attachmentmeans 94, 95 comprises a pair of arms which locate closely with thegroove, permitting the attachment means 94, 95 to move up and down, in adirection parallel to the y-axis. The arms can allow translationalmovement of the anterior femoral cutting block 46 along the rod guide35, along an axis parallel to the y-axis. They also prevent othertranslations or rotations of the anterior femoral cutting block 46.

According to one aspect of the invention, the rod guide 35 acts as ahousing for a sliding bushing 40 (FIGS. 13A to 13D), which bushing 40 isprovided with a hole 41 through which the IM rod 38 passes. The bushing40 fits tightly in the rod guide 35, while permitting free upward 36 ordownward 37 movement by the bushing 40. The bushing may be disposed witha protrusion 42, which seats in one of the slots 44 present in the rodguide 35. The slot-seated protrusion prevents free rotation of acylindrical bushing 40, so the bushing hole 41 is always aligned withthe rod guide slot 44. This means the surgeon is not burdened withrotating a cylindrical bushing 40 in the rod guide 35 to find the hole41. It also allows the surgeon to orient the bushing correctly to obtainthe indicated angle. The protrusion 42 may be sufficiently narrow topermit a limited rotation by the bushing in the rod guide 35; this wouldallow some yawing by a posterior femoral cutting block 29 as describedbelow and as indicated in FIG. 19, 76. The bushing hole 41 couplestightly with the IM rod 38.

The bushing hole 41 passes in the direction of the transverse axis ofthe bushing 40; the transverse axis (B-B′, FIG. 13A) is perpendicular tothe longitudinal (A-A′ axis, FIG. 13B to 13C). According to one aspectof the invention, the central axis of the hole 41 is aligned with thetransverse axis B-B′ of the bushing 40. According to another aspect ofthe invention, the axis of the central axis of the hole crosses thetransverse axis B-B′ of the bushing 40 at an angle of 0, 1, 2, 3, 4, 5,6, 7, 8, 9, 10, 11, 12, 13, 14 or 15 deg, or an angle in between any twoof the aforementioned angles. For the required angle, a unique bushing40 may be provided. Examples of separate bushing are shown in FIGS. 13B(hole 41′ at 0 deg), 13C (hole 41″ at 3 deg) and 13D (hole 41″′ 5 deg).To achieve the angles of −1, −2, −3, −4, −5, −6, −7, −8, −9, −10, −11,−12, −13, −14 or −15 deg, the bushing 40 may be inserted into the rodguide 35 in the opposing direction i.e. rotated 180 deg around axisA′A′. Alternatively, when a bushing cannot be rotated, theaforementioned negative angles may also be provided by virtue ofseparate bushings. A range of angles provided by a plurality of bushings40 gives the surgeon the choice to fine tune the cutting angle.

A further embodiment of the present invention is a posterior femoralcutting block 29, disposed with one or more holes 56, 57 the centralaxis of which lies in an axis parallel to the y-axis (FIG. 11A). Saidholes may be configured to receive an attachment means 48′, 48″ of ananterior femoral cutting block 46 (FIG. 15). Said holes may also beconfigured to receive an attachment means 52, 55 of an distal femoralcutting block 50 (FIG. 17). Preferably there are two holes locatedeither side of the rod guide 35. Preferably the holes are cylindrical.

The holes allow the posterior femoral cutting block 29 to attachsecurely to the anterior femoral cutting block 46. When the attachmentmeans 48′, 48″ is rod shaped as shown in FIG. 15, it may couple closelywith the walls of the hole, permitting the attachment means 48′, 48″ tomove up and down, in a direction parallel to the y-axis. The position ofthe anterior femoral cutting block 46 on the posterior femoral cuttingblock 29 may be locked by means of a threaded tightening bolt 88 thatcontacts the attachment means 48′, 48″ upon tightening through athreaded hole 90. Alternatively or in addition, the position of theanterior femoral cutting block 46 on the posterior femoral cutting block29 may be locked by means of a sprung bolt that can releasably contactthe attachment means 48′, 48″. The sprung bolt can be engaged orretracted by, for example, turning a knob 91. The sprung bolt allows thesurgeon to adjust finely the position of the anterior femoral cuttingblock 46 prior to locking the final position with the tightening bolt.

The posterior femoral cutting block 29 is temporarily attachable to thealignment device 26. Once the cutting block is properly aligned, thealignment device 26 can be removed, leaving the cutting block in place,held, for example, by securing pins driven into the femur. For thispurpose, the posterior femoral cutting block 29 may be provided with oneor more holes running from the front 33 to the back 34 of the blockthrough which securing pins can be inserted and driven in to the femur.With the removal of the alignment device, the surgeon's view and freedomof movement is unobstructed, so enabling efficient resectioning usingthe mounted posterior femoral cutting block 29.

One preferred embodiment of the invention is a posterior femoral cuttingblock 29 as described above comprising two or more holes 56, 57 thecentral axis of which lies in an axis parallel to the y-axis. The holesare configured to receive two or more attachment means 52, 55 of adistal femoral cutting block 50 such that a plane of the blade guide 51of the distal block 50 is aligned with the x-y plane. The plane of ablade guide is the plane adopted by a blade when inserted into a bladeguide. The same holes may also be configured to receive two or moreattachment means 48′, 48″ of an anterior femoral cutting block 49 suchthat a plane of the blade guide 47 of the anterior block 46 is alignedwith the x-z plane.

The plane of blade guides 31, 32 of the posterior femoral cutting block29 may or may not be exactly parallel with the blade guide 47 of theanterior femoral cutting block 46. Often the prosthesis will fit onto afemur head where the anterior and posterior femoral cuts are angled in awide V-shape. To achieve this, the planes of the blade guides of theanterior 49 and posterior 29 femoral cutting blocks may be aligned withthe x-z plane, but set at an angle thereto around the x-axis.

In one embodiment of the invention, the plane of a blade guide 31, 32 ofthe posterior femoral cutting block 29 is aligned with the x-z plane,and set at an angle of −10, −9, −8, −7, −6, −5, −4, −3, −2, −1, 0, 1, 2,3, 4, 5, 6, 7, 8, 9, 10 deg around the x-axis.

The combination of the alignment device 26 and the cutting block 29 asdescribed herein allows the surgeon to align precisely the cutting blockin two critical ways: laterally along the y-axis and according to anangle of rotation around the x-axis. No other adjustment is necessary asthe inventors have found. The invention provides the surgeon with anaccurate and convenient tool for accurately resection the femur.

Other Cutting Blocks

The posterior femoral cutting block 29 being accurate placed, acts as areferencing block for aligning the other cutting blocks used during kneeprosthetic surgery, namely the anterior femoral cutting block 46, andthe distal femoral cutting block 50.

Anterior Femoral Cutting Block

Reference is made in the following description to FIGS. 14A to 14D and15. During prosthetic knee surgery, a cut to the bone is made parallelto the posterior femoral cut i.e. an anterior femoral cut. Accordingly,the present invention provides an anterior femoral cutting block 46(FIG. 15) disposed with a blade guide 47, said block provided with anattachment means 48′, 48″ for attaching to the posterior femoral cuttingblock 29, which means 48′, 48″ is configured to align the blade guide 47parallel with the blade guides 32 of the posterior femoral cutting block29.

According to a preferred embodiment of the invention, the anteriorfemoral cutting block 46 comprises one or more attachment means 48, 48″which are configured to couple with one or more reciprocally positionedholes 56, 57. The attachment means 48′, 48″ may be rod shaped as shownin FIG. 15, which allows a close couple with the walls of the hole,permitting the attachment means 48′, 48″ to move up and down, in adirection parallel to the y-axis within the hole. It may also preventother translations or rotations of the anterior femoral cutting block46. Optionally, the attachment means 48′, 48″ can be disposed with alocking mechanism that holds the anterior femoral cutting block 46 inplace once the appropriate position along the y-axis is found.Preferably there are two attachment means, configured to couple with areciprocating pair of holes located either side of the rod guide 35.Preferably an attachment means is a cylindrical rod.

FIG. 14A depicts an anterior femoral cutting block 46 attached in situon a posterior femoral cutting block 29 via attachment means 48′. Theanterior femoral cutting block 46 may be translated in a directionparallel to the y-axis, relative to the posterior femoral cutting block29. The desired adjustment can be read using a distance reader 92present on the anterior femoral cutting block 46 against a set ofgraduation present on the posterior femoral cutting block 29. Once thefinal position is obtained, the anterior femoral cutting block 46 can belocked using a threaded bolt 88. FIG. 14B depicts the anterior femoralcutting block 46 attached in situ on a posterior femoral cutting block29 in situ, and the a cutting blade 86 making a section of a posteriorfemoral condyle. FIG. 14C depicts the anterior femoral cutting block 46attached in situ on a posterior femoral cutting block 29 in situ, andthe a cutting blade 86 making a section of a anterior femoral condyle.FIG. 14C is a photograph from an operation where the anterior femoralcutting block 46 attached in situ on a posterior femoral cutting block29 in situ, and the a cutting blade 86 making a section of a posteriorfemoral condyle.

One embodiment of the present invention is an anterior femoral cuttingblock 46 disposed with one or more rod shaped attachment means 48, 48″which are configured to couple with one or more reciprocally positionedholes 56, 57 on the posterior femoral cutting block, permitting theanterior femoral cutting block 46 to move up and down, in a directionparallel to the y-axis.

According to a another embodiment of the invention, the attachment means94, 95 (FIG. 14D) comprises two arms which grip the rod guide 35.Similarly, the rod guide 35 may be disposed with outer grooves 66 thatreceive the attachment means 94, 95 along which the anterior femoralcutting block 46 can be positioned in an axis parallel to the y-axis.The arms can allow translational movement of the anterior femoralcutting block 46 along the rod guide 35, along an axis parallel to they-axis. The longitudinal axis of the arms 94, 95 are aligned with thex-y plane. They also prevent other translations or rotations of theanterior femoral cutting block 46. Optionally, the attachment means 94,95 can be disposed with a locking mechanism that holds the anteriorfemoral cutting block 46 in place once the appropriate position alongthe y-axis is found.

The plane of blade guide 47 of the anterior femoral cutting block 49 mayor may not be exactly parallel with the blade guides 31, 32 of theposterior femoral cutting block 29. Often the prosthesis will fit onto afemur head where the anterior and posterior femoral cuts are angled in awide V-shape. To achieve this, the planes of the blade guide of theanterior 49 femoral cutting block may be aligned with the x-z plane, butset at an angle thereto around the x-axis.

In one embodiment of the invention, the plane of blade guide 47 of theanterior femoral cutting block 49 is aligned with the x-z plane, and setat an angle of −10, −9, −8, −7, −6, −5, −4, −3, −2, −1, 0, 1, 2, 3, 4,5, 6, 7, 8, 9, 10 deg around the x-axis.

To assist the surgeon, the rod guide 35 may be provided with graduations49 against which the distance move anterior femoral cutting block 46 canbe measured. The anterior femoral cutting block may by provided with oneor more distance readers 92, 93. So the cut corresponds with theposterior cut, a set of graduations 59, may also be provided on thealignment device 26 to indicate the level of the posterior femoralcutting block 29. By reading the graduations 59, 59′ present on thealignment device 26, the height of the anterior femoral cutting block 46can be accurately set.

Distal Femoral Cutting Block

The following description is made with reference to FIGS. 16A to 16C and17. During prosthetic knee surgery, a cut to the bone is madeperpendicular to the posterior femoral cut i.e. a distal femoral cut ismade. Accordingly, the present invention provides a distal femoralcutting block 50 disposed with a blade guide 51, said block providedwith an attachment means 52, 55 for joining the block to the posteriorfemoral cutting block 29, which means 52, 55 is configured to align theplane of the blade guide 51 with the x-y plane.

According to a preferred embodiment of the invention, the distal femoralcutting block 50 comprises two or more attachment means 55, 52 whichlocate in two or more complementary holes 56, 57 present on theposterior femoral cutting block 29. Preferably there are two attachmentmeans 55, 52, configured to couple with a reciprocating pair of holeslocated either side of the rod guide 35. Preferably an attachment meansis a cylindrical rod.

The attachment means 52, 55 fixes the position and orientation of thedistal cutting block 50 relative to the posterior femoral cutting block29. Consequently, the blade guide 51 is non-adjustable. The distance ofthe distal cut, therefore, is selected by providing a range of distalcutting blocks 50 where the blade guide 51 is set at a differentdistance, which distance can be marked on the distal cutting block 50.The surgeon may select the appropriate distal cutting block according tothe distances required. Readings 59 from the alignment device 26, andfrom the readings 49 used to position the anterior femoral cutting block46 can be used to find the required distance. Fine tuning to thedistance may be achieved by providing the posterior femoral cuttingblock 29 with additional holes which, depending which are used, move thedistal cutting block 50 closer or further from the distal end of thefemur 1. The fine adjustment provided by the choice holes can be marked60 on the distal cutting block 50 for reference by the surgeon.

FIG. 16A depicts a distal cutting block 50 prior to attachment to theposterior femoral cutting block 29. Two attachment means 55, 52,configured to couple with a reciprocating pair of holes located eitherside of the rod guide on the posterior femoral cutting block 29. FIG.16B depicts a distal cutting block 50 after attachment to the posteriorfemoral cutting block 29; the distal cutting block 50 is held in placeusing pins 53 driven into the femur. FIG. 16C depicts a distal cuttingblocks 50 dismounted from the posterior femoral cutting block 29 andheld in place using said pins 53. The condyles are sectioned in thisarrangement, using a cutting blade 96 guided through the blade guide 51.

The plane of blade guide 51 of the distal femoral cutting block 50 mayor may not be exactly perpendicular with the blade guides 31, 32 of theposterior femoral cutting block 29. The blade guide of the distalfemoral cutting block 50 may be aligned with the x-y plane, but set atan angle thereto around the x-axis.

In one embodiment of the invention, the plane of blade guide 51 of thedistal femoral cutting block 50 is aligned with the x-y plane, and setat an angle of −10, −9, −8, −7, −6, −5, −4, −3, −2, −1, 0, 1, 2, 3, 4,5, 6, 7, 8, 9, 10 deg around the x-axis.

Kit

The present invention may includes a kit comprising one or more of theaforementioned parts.

One embodiment of the present invention is a kit comprising one or moreof the following components:

-   -   at least one (e.g. 1, 2, 3, 4 or 5) spacing means such as for        example, the above described pin 17 and keeper 85 assembly,    -   a tibial plate 7 provided with a receiving slot,    -   an alignment device 26,    -   a posterior femoral cutting block 29,    -   an anterior femoral cutting block 46,    -   a distal femoral cutting block 50,

It may also comprise a femoral chamfered cutting block, such block beingwell known in the art.

It may also comprise instructions for use. The kit may also be providedwith one or more knee prosthesis.

The kit may provide components specific to a particular size of femurand prostheses. Alternatively, it may provide a range of differentsizes, to accommodate different bone and prostheses sizes. For examplethe kit may provide a range of a distal femoral cutting blocks 50 or arange of differently sized prostheses.

The material used to manufacture the above described device maybe anysuitable material that is compatible for use in surgical instruments.Examples include surgical stainless steel, titanium, carbon fibre,nickel alloys, plastics, polymers etc.

Method for Performing Knee Prosthesis Surgery

The present invention also encompasses a method for performingprosthetic knee surgery, which method is based around tensioning theknee joint while in flexion, without moving the patella to one side. Theinventors have found that by pre-tensioning the joint in this way, thefemoral bone cuts made after the patella is moved to one side are soaccurate that the soft tissue balancing is avoided altogether orreduced.

One embodiment of the present invention is a method for performingreplacement prosthetic knee surgery, after fitting a tibial plate 7,comprising the steps:

-   -   tensioning the knee joint while in flexion, and while the        patella is in place to obtain or reproduce the correct flexion        gap,    -   maintaining the tension using an adjustable spacing means        between the fitted tibial plate 7 and the femur, and    -   performing femoral bone cuts after the patella is moved to one        side. The method is suitable for performing after the tibial        plate 7 has been fitted.

Preferably, the spacing means enters the femur 1 through the anteriorregion 61 of the femoral condyle and exits though the posterior end 62of the condyle. The spacing means applies or maintains pressure betweenthe fitted tibial plate 7 and the femur, so the flexion gap 4 is set tothe appropriate level.

Thus, another embodiment of the invention is a method as describedherein, further comprising the steps of:

-   -   making a hole (10, 11) in each femoral condyle, which hole        passes through the anterior region (14) of the femoral condyle        and exits though the posterior end (15),    -   inserting said spacing means through said holes (10, 11), to        introduce said spacing means into the flexion gap while the        patella is in place.

In one embodiment of the invention, the flexion gap is adjusted by meansof an inflatable balloon disposed with an inflation tube. The balloonmay be inflation by air or fluid passing through the inflation tube. Theuninflated balloon is inserted into in the space between the femoralcondyles 5, 6 and tibial plate 7. It is generally not inserted throughthe hole 10, 11 that passes from the anterior 14 end of a femoralcondyle 5, 6 through to the posterior 15 end of said condyle 5, 6.Instead, it may be inserted into the gap through a natural distalopening. By inflating the balloon, tension can be applied between thefemoral condyles 5, 6 and tibial plate 7. Once the correct gap isachieved, the gap is maintained by the aforementioned spacing means.

The balloon and inflation tubing can be made from any suitable materialsuch as found in a balloon catheter, for example. The balloon may bemade from latex and the tubing may be made from polypropylene. Theskilled person can readily prepare such an inflatable balloon based on aballoon catheter design from methods known in the art.

The knee is in flexion while the gap is maintained and the alignmentdevice applied. The angle of flexion may be 70, 71, 72, 73, 74, 75, 76,77, 78, 79 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94,95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109,110 deg, or an angle in the range between any two of the aforementionedvalues. It is preferably 90 deg.

FIG. 18 depicts a view of a knee after the joint has been tensionedaccording to the present method; the patella has been moved aside. Thespacing means comprises a set of pins 18 as already described above.Each pin enters the femur 1 through the anterior region 61 of thefemoral condyle. Each pin 18 exits though the posterior end 62 of thecondyle and is threaded in this part, which thread is engaged by akeeper 85. The surgeon will have adjusted the spacing means by turningthe pin 18 via an hexagonal coupling 21 until the pin contacts thefitted tibial plate 7, and adjusts the flexion gap 4 to the appropriatedegree.

With reference to FIG. 19, another embodiment of the present inventionis the method as described above, further comprising the step ofattaching the posterior femoral cutting block 29 to the tibial plate 7using an alignment means which permits movements by the posteriorfemoral cutting block 29 along a y-axis, along an x-axis, and rotationabout the x- and y-axes relative to a static tibial plate, where they-axis is parallel to the intermedular tibial axis, and the x-axis isperpendicular to the plane of the y- and z-axes, where the z-axis isparallel to the intermedular femoral axis. Such alignment means may bean alignment device 26 as described above. Of course, prior toattachment, the patella is moved aside.

FIG. 19 shows a photograph of a knee after the step of attaching theposterior femoral cutting block 29 to the tibial plate 7, using themeans described above, which is an alignment device 26. The alignmentdevice 26 permits the movement of the cutting block 29 in the along ay-axis, which movement is indicated by arrow 81, and around an x-axis,which movement is indicated in one direction by arrow 80, and around ay-axis which movement is indicated in one direction by arrow 76. Thealignment device 26 also permits movement by the block 29 along anx-axis, which movement is indicated in one direction by arrow 63 in FIG.20. Note the movement along the x-axis allows the cutting block to mountan IM rod, regardless of the placement of the coupling means 24. Oncethe IM rod 38 has been mounted, movement along the x-axis (direction 63,FIG. 20) becomes restricted. The movements permitted by the alignmentdevice allow the surgeon accurately to cut the posterior femoralcondyles, and measure the depth of the cut.

With reference to FIG. 21, another embodiment of the present inventionis the method as described above, further comprising the step ofsecuring the posterior femoral cutting block 29 to the femur in thealigned position using pins 65′, 65″ inserted into the posterior femoralcutting block 29 and driven into the femur. Once secured, the anteriorfemoral cutting block 46 can be attached as described below, and thenthe alignment means 26 removed.

With reference to FIGS. 14A to 14D, and 22, another embodiment of thepresent invention is a method as described above, further comprising thestep of attaching an anterior femoral cutting block 46 disposed with ablade guide 47 to the posterior femoral cutting block 29, using a meanswhich aligns the blade guide 47 parallel with the blade guides 32 of theposterior femoral cutting block 29, and allows translational movement ofthe anterior femoral cutting block 46 along the rod guide 35, along anaxis parallel to the y-axis. Such means 48′, 48″ can be a pair of rodsas described above.

The surgeon may reference the height of the anterior femoral cuttingblock 46 according to the height of the posterior femoral cutting block29. He may find the correct cutting height, by using graduations 49 onthe rod guide 35 against which the distance moved by the anteriorfemoral cutting block 46 can be measured. By reading the graduations 59present on the alignment device 26, the height of the anterior femoralcutting block 46 can be accurately set.

With the removal of the alignment means (FIG. 14A to D cf FIG. 22), thesurgeon's view and freedom of movement is unobstructed, so enablingefficient resectioning using the mounted posterior femoral cutting block29 and anterior femoral cutting block 46.

With reference to FIG. 16A to 16C, another embodiment of the presentinvention is a method as described above, further comprising the step ofattaching a distal femoral cutting block 50 disposed with a blade guide51 to the posterior femoral cutting block 29, using a means which alignsthe blade guide 47 with the x-y plane as mentioned above, and fixes theposition and orientation of the distal cutting block 50 relative to theposterior femoral cutting block 29. The anterior femoral cutting block46 may be present or may be removed prior to attachment.

The distance of the distal cut can be selected as described above, froma range of distal cutting blocks 50 where the blade guide 51 is set atdifferent distances. The surgeon may select the appropriate distalcutting block according to the distances 59 read from the alignmentdevice 26, and from the distances 49 used to position the anteriorfemoral cutting block 46. The surgeon may also optionally choose theangle of the plane of the blade guide. After alignment, the distalcutting block 50 can be attached to the femur using pins 53 insertedthrough holes in the in said block and driven into the femur (FIG. 16B).After securement, of the distal cutting block 50, the posterior femoralcutting block 29. With the removal of the posterior femoral cuttingblock 29 (FIG. 16C), the surgeon's view and freedom of movement isunobstructed, so enabling efficient resectioning using the secureddistal cutting block 50.

Once the posterior, anterior and distal femoral condyles have been cut,femur is left with three flat faces, giving an essentially square-headedprofile for receiving the prosthesis. The head may be made polygonal(e.g. with five faces) by removing two of the corners. This can beachieved with the use of a femoral chamfered cutting block which fitsover the anterior, posterior and distal edges of the square-headedfemur, and is provided with blade guides at the appropriate angles (e.g.at 45 deg to each square face). Such cutting blocks and procedures aregenerally known.

The presently described method may include several intervening stepswhich would be known to the person skilled in the art.

What is claimed is:
 1. A removable elongate device for assistingprosthetic knee surgery by maintaining a correct flexion gap between afemur and a tibia of a human knee in flexion where the tibia is fittedwith a tibial plate, said device comprising: one elongate member that isa pin provided with a threaded region at one end of said pincontinuously extending longitudinally along at least part of theelongate member, and at the other end with a non-threaded regionextending longitudinally along part of the elongate member andterminating in a coupling element configured to fittingly engage with atool and for transmission of torque to the elongate member and with aminimum outer radial dimension equal to or smaller than that of the pin,which pin is of dimensions for introduction at its threaded end througha hole that passes from the anterior end of a human femoral condylethrough to the posterior end of said condyle and wherein the pin spansat least the length of the said hole, and only one keeper correspondingto the one elongate member, the keeper provided with a threaded hole fordirect engagement with the threaded region of said pin, the holeextending from an essentially flat and planar upper surface of thekeeper and terminating at an essentially flat and planar lower surfaceof the keeper, said keeper configured for insertion into the flexion gapand to abut with the posterior end of said condyle allowing the threadedregion to advance through the keeper from the upper surface to the lowersurface and protrude from the posterior end of said condyle into theflexion gap by an amount at least equal to the flexion gap and tocontact the tibial plate, wherein the elongate member and the keepercomprise a biocompatible material, wherein the keeper is configured toretain an essentially fixed orientation relative to the femur, andwherein the keeper is provided with two or more separated regionscontaining a plurality of protrusions each extending beyond the uppersurface and each narrowing from a base end in connection with the uppersurface to a top end, and configured to retain the keeper in theessentially fixed orientation relative to the femur and wherein thekeeper is dimensioned for enclosure within the flexion gap of the humanknee in flexion with the patella in place, wherein the removableelongate device is an intra-articular distractor.
 2. The deviceaccording to claim 1, wherein the keeper is configured for frictionallyengaging with the femur.
 3. The device of claim 1, wherein theprotrusions comprise a tapered shape.
 4. The device of claim 3, whereinthe protrusions comprise a pyramid shape.
 5. The device of claim 3,wherein the top end of each protrusion is pointed.
 6. The device ofclaim 1, wherein the two or more separated regions comprise: a firstpair of separated regions corresponding with a first and secondplurality of protrusions, respectively, positioned along a first edge ofthe keeper; and a second pair of separated regions corresponding with athird and fourth plurality of protrusions, respectively, positionedalong a second, opposing edge of the keeper.
 7. The device of claim 6,wherein a first axis extends through the first and second plurality ofprotrusions, and a second axis extends through the third and fourthplurality of protrusions, wherein the threaded hole is offset from andpositioned between the first and second axes.
 8. The device of claim 7,wherein a third axis extends approximately longitudinally to the firstand second axis, and through the threaded hole, wherein there are noprotrusions positioned on the third axis.
 9. The device of claim 8,wherein a fourth axis extends approximately parallel to the first andsecond axis, and through the threaded hole, wherein there are noprotrusions positioned on the fourth axis.
 10. A kit comprising two ofthe removable elongate devices according to claim
 1. 11. A kitcomprising: the device of claim 1, and one or more of the following: analignment device for aligning a block for cutting the posterior femoralcondyles during prosthetic knee surgery, a posterior femoral cuttingblock, an anterior femoral cutting block, and a distal femoral cuttingblock.
 12. The kit of claim 11 comprising: the alignment device, whereinsaid alignment device comprises: (i) a securing means for temporaryattachment to the fitted tibial plate, which securing means fixes theposition and orientation of the alignment device relative to the tibialplate, (ii) a coupling means for temporary attachment to the posteriorfemoral cutting block, which coupling means prevents rotation of theposterior femoral cutting block, around a z-axis, where the z-axis isparallel to the intermedular femoral axis, and (iii) an extending meansjoining (i) and (ii), which extending means is configured to adjust thedistance between (i) and (ii) along a y-axis, where the y-axis isdefined as being parallel to the intermedular tibial axis.
 13. The kitof claim 12 wherein the securing means comprises a pair of pinsconfigured for insertion into a corresponding pair of holes present onthe edge of the tibial plate.
 14. The kit of claim 12 wherein saidcoupling means permits displacement of the posterior femoral cuttingblock parallel to an x-axis.
 15. The kit according to claim 12, whereinsaid coupling means is a finger-like protrusion having an upper surfacedisposed with a flat groove, which groove is configured to engage with apointed ridge of a receiving elongate slot present in said posteriorfemoral cutting block.
 16. The kit according to claim 12 wherein saidextending means is connected to the coupling means by way of acylindrical coupling that permits rotation of the posterior femoralcutting block around the y-axis.
 17. The kit according to claim 12wherein the extending means comprises a rack-and-pinion assembly wherethe rack element carries the coupling means, while the pinion carriesthe securing means, or vice versa.
 18. The kit according to claim 11comprising: the posterior femoral cutting block, wherein said posteriorfemoral cutting block comprises one or more blade guides, furthercomprising a receiving slot configured to receive a coupling meansattached to an alignment device, wherein said alignment devicecomprises: (i) a securing means for temporary attachment to the fittedtibial plate, which securing means fixes the position and orientation ofthe alignment device relative to the tibial plate, (ii) a coupling meansfor temporary attachment to the posterior femoral cutting block, whichcoupling means prevents rotation of the posterior femoral cutting block,around a z-axis, where the z-axis is parallel to the intermedularfemoral axis, and (iii) an extending means joining (i) and (ii), whichextending means is configured to adjust the distance between (i) and(ii) along a y-axis, where the y-axis is defined as being parallel tothe intermedular tibial axis.
 19. The kit according to claim 18 whereina plane of said one or more blade guides is aligned with an x-z plane,and set at an angle of between −10 and +10 deg around an x-axis.
 20. Thekit according to claim 18, wherein the receiving slot runs parallel tothe blade guides, and connects a front of the block to a back of theblock.
 21. The kit according to claim 18, wherein said receiving slot iswider than the coupling means, allowing the posterior femoral cuttingblock to move parallel to an x-axis relative to the coupling means wherethe x-axis is perpendicular to a y-z plane.
 22. The kit according toclaim 18, further comprising an intramedular fermoral rod guide, whichrod guide comprises an elongate slot oriented perpendicular to saidreceiving slot, and is configured to receive an intramedular femoralrod, IM rod.
 23. The kit according to claim 22, wherein the rod guide isconfigured to receive a sliding bushing, which bushing is provided witha hole through which the IM rod passes.
 24. The kit according to claim23, wherein a central axis of said hole crosses a transverse axis (B-B′)of the bushing by angle between −15 and 15 deg.
 25. The kit according toclaim 22, further comprising a bushing, which bushing is provided with ahole through which the IM rod passes.
 26. The kit according to claim 22,wherein said rod guide is an elongate structure perpendicular to thewidth of the receiving slot and disposed with one or more outer groovesrunning in an axis parallel to the y-axis, said grooves configured toreceive an attachment means of said posterior femoral cutting block. 27.The kit according to claim 18, comprising two or more holes, the centralaxis of which lie in an axis parallel to the y-axis, configured toreceive two or more attachment means of an anterior femoral cuttingblock and distal femoral cutting block, such that a plane of the bladeguide of the anterior block aligns with an x-z plane and a plane of theblade guide of the distal block aligns with an x-y plane.
 28. The kitaccording to claim 11 comprising the anterior femoral cutting block,wherein the anterior femoral cutting block is disposed with a bladeguide, said block provided with an attachment means for attaching to theposterior femoral cutting block, which means is configured to align aplane of the blade guide with an x-z plane.
 29. The kit according toclaim 28 wherein said plane is set at an angle between −10 and +10 degaround an x-axis.
 30. The kit according to claim 11 comprising thedistal femoral cutting block, wherein said distal femoral cutting blockis disposed with a blade guide, said distal femoral cutting block isprovided with an attachment means for joining the distal femoral cuttingblock to the posterior femoral cutting block, which means is configuredto align a plane of the blade guide with an x-y plane.
 31. The kitaccording to claim 11 further comprising the tibial plate, the alignmentdevice comprising a securing means, wherein said tibial plate includes areceiving slot for receiving said securing means.
 32. The kit accordingto claim 11, further comprising a knee prosthesis.
 33. The kit of claim11, comprising: the alignment device, and the posterior femoral cuttingblock.